Add Prettier for TypeScript formatting

- Install prettier
- Configure .prettierrc.json and .prettierignore
- Add npm scripts: format, format:check
- Add Makefile target: format-frontend
- Format all frontend files

frontend/app/sum/page.tsx

@@ -21,7 +21,7 @@ export default function SumPage() {
     const numA = parseFloat(a) || 0;
     const numB = parseFloat(b) || 0;
     setError(null);
-    
+
     try {
       const data = await api.post<{ result: number }>("/api/sum", { a: numA, b: numB });
       setResult(data.result);
@@ -58,7 +58,7 @@ export default function SumPage() {
       <div style={styles.content}>
         <div style={styles.card}>
           <span style={styles.label}>Sum Calculator</span>
-          
+
           {!showResult ? (
             <div style={styles.inputSection}>
               <div style={styles.inputRow}>
@@ -84,17 +84,11 @@ export default function SumPage() {
                   />
                 </div>
               </div>
-              <button 
-                onClick={handleSum} 
-                style={styles.sumBtn}
-                disabled={a === "" && b === ""}
-              >
+              <button onClick={handleSum} style={styles.sumBtn} disabled={a === "" && b === ""}>
                 <span style={styles.equalsIcon}>=</span>
                 Calculate
               </button>
-              {error && (
-                <div style={styles.error}>{error}</div>
-              )}
+              {error && <div style={styles.error}>{error}</div>}
             </div>
           ) : (
             <div style={styles.resultSection}>